The NFL, compared with other football leagues, is notorious for being very hard to predict. Betting lines in the leagues are usually tight, with favorites typically expected to win by 4 points or less. However, you will often see underdogs win outright and sometimes you will even see blowouts out of nowhere, with teams winning 38-3 or something of the like. More than any other sport, the NFL's gambling lines turn out to be way off and unpredictable. This is because of the competitive nature of the league and the parity of talent between teams.
The competitive margin between the best and worst NFL teams is pretty razor thin. Often times games will come down to 1 or 2 plays and huge upsets can happen, the players are so well trained and have offense and defense down to a science. The players are all similarly big and strong, and most have been playing football their entire lives.
It is no surprise the NFL is as competitive as it is with the amount of money involved. The league is making more money than ever and has been growing significantly over the last decade, with multi billion dollar tv and media deals, and billions more in merchandise revenues annually. In turn, this money flows down to the individual organizations and the owners are incentivized to spend hundreds of millions of dollars to build the best teams they can (restrained by the salary cap of course). The NFL is quite the monopoly that will continue to thrive for years.
